Pursuant to certain industry standards (e.g., the TIA/EIA-568-B.2-1 standard approved Jun. 20, 2002 by the Telecommunications Industry Association), each jack, plug and cable segment in a communications system may include a total of at least eight conductors that comprise four twisted differential pairs. The industry standards specify that, in at least the connection region where the contacts (blades) of a modular plug mate with the contacts of the modular jack (referred to herein as the “plug-jack mating region”), the eight contacts of the jack or plug are aligned in a row and are assigned specific pair numbers.
Local area network (LAN) cables may suffer from many transmission impairments. One such impairment is crosstalk between twisted pairs in a four-pair cable. “Crosstalk” in a communication system refers to unwanted signal energy that is induced onto the conductors of a first “victim” differential pair from a signal that is transmitted over a second “disturbing” differential pair. The induced crosstalk may include both near-end crosstalk (NEXT), which is the crosstalk measured at an input location corresponding to a source at the same location (i.e., crosstalk whose induced voltage signal travels in an opposite direction to that of an originating, disturbing signal in a different path), and far-end crosstalk (FEXT), which is the crosstalk measured at the output location corresponding to a source at the input location (i.e., crosstalk whose signal travels in the same direction as the disturbing signal in the different path). Both types of crosstalk comprise an undesirable noise signal that interferes with the information signal on the victim differential pair.
A variety of techniques may be used to reduce crosstalk in communications systems such as, for example, tightly twisting the paired conductors in a cable, whereby different pairs are twisted at different rates (also known as different “lay lengths”) that are not harmonically related, so that each conductor in the cable picks up approximately equal amounts of signal energy from the two conductors of each of the other differential pairs included in the cable. If this condition can be maintained, then the crosstalk noise may be significantly reduced, as the conductors of each differential pair carry equal magnitude, but opposite phase signals such that the crosstalk added by the two conductors of a differential pair onto the other conductors in the cable tends to cancel out.
In addition, some prior cables have included separators which introduce physical barriers between pairs. These barriers serve to increase the distance between pairs and in turn reduce the amount of crosstalk between the six distinct combinations of pairs. The barrier ay also act as a shield, which may further reduce crosstalk. By way of example, FIG. 1a is a cross-sectional view of a four pair unshielded twisted pair (UTP) cable 20 with no separator. The conductor pairs of the cable 20 are identified with the labels 1, 2, 3 and 4 (for the purposes of this discussion, these pair labels are arbitrary and do not necessarily correspond to the pair designations for jacks and plugs under TIA/EIA-568-B.2-1). In the cable 20 of FIG. 1a, some crosstalk exists between all six different combinations of pairs: namely, between pairs 1-2, 1-3, 1-4, 2-3, 2-4 and 3-4.
FIG. 1b illustrates a cable 20′ that includes a cruciform-shaped separator 30, which is used to increase the distance between all pairs 1-4, thereby resulting in improved crosstalk immunity. Such a separator 30 is typically formed of a polymeric material. An exemplary separator 30 of this type is described in U.S. Pat. No. 5,969,295 to Boucino et al., the disclosure of which is hereby incorporated herein by reference.
FIG. 1c illustrates a cable 20″ in which a flat tape is used as a separator 30′. As can be seen in FIG. 1c, the tape 30′ is arranged such that pairs 1 and 4 are located on one side of the tape 30′ and pairs 2 and 3 are located on the other side of the tape 30′. As a result, the combinations of pairs 1-2, 1-3, 2-4 and 3-4 realize improved crosstalk immunity. An exemplary separator of this type is described in U.S. Pat. No. 6,570,095 to Clark et al., the disclosure of which is hereby incorporated herein in its entirety.